Vorpal Strike

An arc of amethyst energy is unleashed towards a target within range. Make a ranged spell attack against the target. On a hit, the target takes 8d10 force damage. On a miss, the target takes half as much damage.

When you target a creature with this spell and roll a 20 on the attack roll, that target takes an extra 11 force damage. Then roll another d20. if you roll a 20, you severe one of the target's limbs, with the effect of such a loss determined by the DM. If the creature has no limb to sever, you lop off a portion of its body instead. A creature is immune to this effect if it immune to force or slashing damage.

At Higher Levels. When you cast this spell using a spell slot of 7th level or higher, the damage increases by 2d10 for each slot above 6th.